U.S. Pat. No. 4,052,988 describes p-dioxanone homopolymers and the preparation of absorbable filaments exhibiting mechanical and biological properties suitable for use as surgical sutures. Unlike previous absorbable synthetic sutures, for example sutures derived from homopolymers or copolymers of lactide or glycolide, p-dioxanone sutures are particularly well suited for use as monofilament sutures. Monofilament sutures made with p-dioxanone have enhanced flexibility and pliability compared to conventional absorbable synthetics sutures. Conventional absorbable synthetic sutures generally have a braided or twisted construction in a multifilament form to reduce the "stiff" feel of the suture. Unfortunately, multifilament sutures are often disadvantageous because their rough surface can often tear tissue during surgical procedures.
As good as the sutures derived from p-dioxanone are, there is still room for improvement. U.S. Pat. No. 4,643,191 describes copolymers of p-dioxanone and lactide, and absorbable sutures prepared therefrom. The lactide component of the copolymer may offer enhanced physical properties, for example, increased straight or knot tensile strength and reduced modulus, without sacrificing any of the other outstanding properties of a p-dioxanone homopolymer.
U.S. Pat. No. 4,653,497 describes absorbable sutures prepared from copolymers of p-dioxanone and glycolide. The glycolide component of the copolymer significantly increases the rate of in vivo absorption and the in vivo breaking strength retention properties of the copolymer, properties which can be extremely advantageous for certain surgical procedures.
A recent European Patent Application, EPA 460,428 A2, also describes copolymers of caprolactone, glycolide and lactide. This application describes a block copolymer formed by a two-stage polymerization process. In the first stage of this process a prepolymer is formed with a high content of a caprolactone type monomer such as p-dioxanone, the remainder of the prepolymer being a fast reacting glycolide type monomer. In the second stage of the polymerization the prepolymer is reacted with an additional fast reacting glycolide type monomer to provide a segmented block copolymer.
In view of the attempts described in the art to modify or enhance the properties of p-dioxanone homopolymers, it would be desirable to formulate a polymer composition which can offer increased flexibility and a controlled breaking strength retention (BSR) profile.